Include version information in the library

This version information can be queried programmatically by using the
expored opm_core_version symbol.

CMakeLists_files.cmake

@@ -124,6 +124,7 @@ list (APPEND MAIN_SOURCE_FILES
 	opm/core/utility/parameters/tinyxml/tinyxmlerror.cpp
 	opm/core/utility/parameters/tinyxml/tinyxmlparser.cpp
 	opm/core/utility/parameters/tinyxml/xmltest.cpp
+	opm/core/version.c
 	opm/core/wells/InjectionSpecification.cpp
 	opm/core/wells/ProductionSpecification.cpp
 	opm/core/wells/WellCollection.cpp
@@ -213,6 +214,7 @@ list (APPEND PUBLIC_HEADER_FILES
 	opm/core/linalg/blas_lapack.h
 	opm/core/linalg/call_umfpack.h
 	opm/core/linalg/sparse_sys.h
+	opm/core/version.h
 	opm/core/wells.h
 	opm/core/pressure/CompressibleTpfa.hpp
 	opm/core/pressure/FlowBCManager.hpp

opm/core/version.c

@@ -0,0 +1,8 @@
+/* this file is written by the build system; don't include it anywhere else */
+#include <project-version.h>
+
+/* declaration of the externally visible symbol */
+#include <opm/core/version.h>
+
+/* initialization */
+const char* const opm_core_version = PROJECT_VERSION;

opm/core/version.h

@@ -0,0 +1,4 @@
+/**
+ * This symbol is initialized with the built version of the library.
+ */
+extern const char* const opm_core_version;